The automotive industry utilizes belt tensioners to create a generally constant tension on a closed-loop belt as it elongates with wear, wherein the belt is driven by the crankshaft pulley attached to the crankshaft of the engine and wherein the belt rotates two or more driven pulleys each operating an automotive accessory. In known designs, the belt tensioner includes a base secured to the engine, an arm which is adapted to be rotatably-biased and which is rotatably attached to the base, and a tensioner idler pulley which is supported by the arm and which is rotatable about the axis of the tensioner idler pulley. In one known example, the base is a spring case containing a torsion spring which interacts with the spring case and the arm. The arm is rotationally biased (preloaded through spring action) by twisting the arm relative to the base. The tensioner idler pulley on the arm is then placed against the belt. As the belt lengthens under wear, the torque from the preloaded spring continues to cause the tensioner idler pulley of the arm to apply pressure against the belt keeping the belt in tension. The operation of belt tensioners is well known.
Known designs of certain belt tensioners (such as that disclosed in U.S. Pat. No. 6,689,001) include modifying the base of the belt tensioner to include a stop which is located on the base to limit the rotational movement of the arm by contacting a bushing on the arm when the arm rotates towards the stop. Tensioners of this sort are especially useful in drives with combination starter/alternators or other accessories that create excessive belt tension variation.
Still, scientists and engineers continue to seek improved belt tensioners.